Magnetic head having track width defined by trench portions filled with magnetic shield material

ABSTRACT

In a composite magnetic head comprising a magnetoresistive read head including a magnetic thin film having a magnetoresistive effect and soft magnetic members interposing the soft magnetic film between them through a non-magnetic insulation layer, an induction type write head including poles formed in a moving direction of a medium and a conductor crossing the poles, and disposed in the proximity of the magnetoresistive head, and a substrate supporting these heads, the present invention discloses a composite magnetic head characterized in that part of a floating surface inclusive of the magnetic head constituent members has recesses and the read/write operations to and from the medium are effected by the portion interposed by these recesses.

This is a continuation application of application of U.S. Ser. No.10/083,104, filed on Feb. 27, 2002 (now U.S. Pat. No. 6,538,844),continuation application of U.S. Ser. No. 09/598,491, filed Jun. 22,2000, now abandoned), which is a continuation application of U.S. Ser.No. 09/084,321, filed May 26, 1998 (now U.S. Pat. No. 6,111,723), whichis a divisional application of U.S. Ser. No. 08/192,794, filed Feb. 7,1994 (now U.S. Pat. No. 5,850,326), which is a file wrapper continuationapplication of U.S. Ser. No. 07/683,719, filed Apr. 11, 1991, nowabandoned. This application is related to U.S. Ser. No. 09/598,493,filed Jun. 22, 2000 (now U.S. Pat. No. 6,278,578) and U.S. Ser. No.09/598,492, filed Jun. 22, 2000 (now U.S. Pat. No. 6,307,707).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetic head for use in magnetic recordingand to a fabrication method thereof. An embodiment of the presentinvention relates particularly to a read/write magnetic head which issuitable for high density read/write operations.

2. Description of the Prior Art

A conventional magnetic head technology is disclosed in JP-A-59-178609,for example.

A magnetic head of the type in which only a head gap portion projects toa medium direction has been proposed in order to accomplish high densityrecording in magnetic recording. For example, “IEEE TRANSACTION ONMAGNETICS”, Vol. 24, No. 6, November, 1984, pp. 2841-2843, describes amethod of deciding a track width of a magnetic head by applyingmachining from an air bearing surface side.

As to a magnetoresistive head (hereinafter referred to as the “MR head”)used as a read-only magnetic head, too, JP-A-59-71124 and JP-A-1-277313disclose the structure in which only a track width portion (magneticsensing region) is projected to a medium opposing surface.

On the other hand, a read/write magnetic head produced by integratingthe MR head and an induction type write head is known fromJP-A-51-44917, and so forth.

SUMMARY OF THE INVENTION

However, the magnetic head having the structure of the IEEE referencedescribed above involves the problem that off-track performance is lowbecause a flux leaks from regions other than the track width which isdefined by etching. Since a relatively wide region of a slider rail isremoved by etching, floating characteristics of a slider vary greatlybefore and after machining. If etching technique used for an ordinarysemiconductor process is utilized, it becomes extremely difficult tocoat uniformly a resist onto the slider rail, and the problem ofmass-producibility is left unsolved.

The technology disclosed in JP-A-59-71124 and JP-A-1-277313 is not freefrom the following problem. When the MR head only the magnetic sensingregion of which is allowed to project is produced, magnetic shieldlayers that interpose the MR sensor between them from both sides aregreater than the width of projection, so that flux from adjacent trackswhich cross one another through these shield layers results in noise.This invites the problem that a signal-to-noise ratio drops when signalsbecome weaker with a smaller track width.

Furthermore, when a composite magnetic head is produced by combining theMR sensor only the magnetic sensitive region of which projects and theinduction type write head, the width of the write magnetic pole and thatof the projecting portion of the MR sensor deviate from each other dueto a positioning error and the ratio of this deviation to the trackwidth becomes greater with a smaller track width. Therefore, anotherproblem occurs that read efficiency drops. In other words, theconventional MR head described above employs the structure wherein onlythe track width portion is projected to the medium opposing surface soas not to detect signals at portions other than at the read track widthfor the purpose of accomplishing a smaller track width. In theconventional head of this kind an MR sensor pattern only the track widthportion which projects is formed on a substrate and a read head and thelike are formed in such a manner as to align with this projectingportion. Thereafter the substrate is cut and the cut surface is polishedin order to obtain a head only whose projecting portion is exposed to amedium opposing surface. Accordingly, the projecting width of the MRsensor and the width of shield layers and the width of the recordingmagnetic pole and the projecting with the MR sensor do not inevitablycoincide with one another, respectively.

It is a first object of the present invention to provide a narrow trackmagnetic head having excellent off-track performance and a fabricationmethod thereof.

It is a second object of the present invention to provide a magnetichead having a high signal-to-noise ratio.

It is a third object of the present invention to provide a read/writemagnetic head free from a positioning error between a write head and aread head but having a high signal-to-noise ratio.

It is a fourth object of the present invention to provide a fabricationmethod of a magnetic head which reduces the track width of a magnetichead without changing floating characteristics of a slider.

It is a fifth object of the present invention to provide a fabricationmethod of a magnetic head for high density recording having a narrowtrack width at a high fabrication yield.

The first object of the present invention described above can beaccomplished by disposing at least one trench or groove at part of anair bearing surface between a magnetic head and a medium. Moredefinitely, local recesses are defined near a magnetic gap of themagnetic head or its magnetic sensing region so as to define the widthof these members. In one preferred embodiment of the invention, thesetrenches or recesses are formed by focused ion beam (hereinafterreferred to as “FIB”) machining. In another preferred embodiment of theinvention, a material is packed into these trenches or recesses.

The second object of the invention described above can be accomplishedby carrying out track width machining as a bulk from an air bearingsurface side after an MR sensor and shield layers are formed on asubstrate.

The third object of the invention described above can be accomplished byforming a write head and a read head on a substrate and then carryingout track width machining by etching from a polished and cut surface inorder to prevent the track position error between the write head and theread head. In other words, while only the track width portion of a softmagnetic film of each of the write and read heads constituting themagnetic head is left on a floating surface, the other portions areremoved in such a manner as to increase the distance from the medium. Atthe same time, track width machining is applied also to the shield layerof the read head so that only the projecting portion is exposed on thefloating surface. In still another preferred embodiment of the presentinvention, a stopper material for etching is disposed in advance on amachining portion in a head lamination process in order to prevent theexposure of a planarization layer that covers the coil of the write headand a coil when machining is made from the floating surface.

The fourth object of the invention described above can be accomplishedby machining part of a rail of an air bearing surface of a head sliderby use of a focused ion beam.

The fifth object of the invention described above can be accomplished bymachining the shape of the magnetic head by use of a beam having focusedenergy without coating a resist onto the slider rail.

When at least one trench is disposed at part of the air bearing surfaceof the magnetic head with the medium, a magnetic flux does not leak fromregions other than from the track width region defined by the trench.Accordingly, a narrow track magnetic head having high off-trackperformance can be provided.

Yield and accuracy of machining can be improved by using a focused ionbeam when the trench is formed only at part of the air bearing surface.

The leak of the flux can be reduced further by packing a material intothe trench described above.

After the MR sensor and the shield layer are formed on the substrate,track width machining is carried out as a whole from the air bearingsurface side with respect to the medium and in this manner, the width ofthe shield layer can be made substantially equal to the projecting widthof the MR sensor. Accordingly, the flux from adjacent tracks does notmix through the shield layer, resulting in no noise, so that a magnetichead having a high signal-to-noise ratio can be obtained.

In the present invention, the distance between the members inclusive ofthe magnetic shield layer and the medium and between themagnetoresistive sensor and the medium, that is, the spacing, is greatat the portions other than the projecting portion which functions as themagnetic sensing region. Accordingly, the signals from the portionsother than the magnetic sensing region can be reduced remarkably. When afloating distance is 0.15 μm and a move-back distance is 2 μm, forexample, a signal from adjacent tracks can be reduced by at least −50 dBwith respect to a signal at a recording wavelength of 2 μm. Since theportions other than the magnetic sensing region are thus moved back, thenoise resulting from the adjacent tracks can be reduced drastically.

Positioning of the track width between the write head and the read headcan be made extremely precisely by carrying out track width machining ofboth of the heads simultaneously and as a bulk. If an etching stopper isused, an etching margin can be increased even when FIB is not used.

If the projecting portion is formed by utilizing focused ion beametching (FIB) or if a method which defines a trench at part of theslider rail of the head is employed, a trench having a large aspectratio can be formed in a very small region. Consequently, machining doesnot exert adverse influences on the floating characteristics of theslider.

If the shape of the magnetic head is machined by a beam having focusedenergy without coating a resist onto the slider rail, a desired shapecan be machined at a high yield. Furthermore, since an electricallyconductive layer can be formed inside the trench thus formed, a magneticshield material can be packed easily into the trench by field plating orthe like, and a head having high off-track performance can befabricated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a magnetic pole portion of a head inaccordance with the present invention;

FIG. 2 is a diagram showing the field distribution of the magnetic headof the present invention;

FIG. 3 is a diagram showing the frequency dependence characteristics ofHx of the magnetic head of the present invention;

FIG. 4 is a diagram showing comparatively off-track performance of themagnetic head of the present invention and off-track performance of aconventional magnetic head;

FIG. 5 is a diagram showing the relation between the change of a readoutput of the magnetic head of the present invention and a track width;

FIG. 6 is a diagram showing the relation between an incident angle ofFIB used in the fabrication method of the present invention andoff-track performance;

FIG. 7 is a diagram showing the change of read/write characteristicswhen portions other than the magnetic poles of a slider rail aremachined uniformly by FIB;

FIG. 8 is a diagram showing the write characteristics of a vertical headobtained by the present invention;

FIGS. 9A and 9B are perspective views showing the portions near a gapportion of the magnetic head of the present invention;

FIG. 10 is a diagram showing the sensitivity distribution of an MR headin the direction of a track width;

FIGS. 11A and 11B are perspective views of a read/write composite headin accordance with another embodiment of the present invention;

FIGS. 12A and 12B are perspective views of a read/write composite headin accordance with still another embodiment of the present invention;

FIG. 13 is a plan view of a thin film magnetic write head in a firstembodiment of the present invention;

FIG. 14 is a sectional view taken along line A-A′ of the magnetic coreshown in FIG. 13;

FIG. 15 is a sectional view of a conventional magnetic core when viewedin the same way as in FIG. 14;

FIGS. 16 and 17 are sectional views of the magnetic core in otherembodiments of the present invention, respectively;

FIG. 18 is a diagram showing the measurement result of characteristicsand showing the relation between a write density and a read output in aconventional head and in a head of the present invention, respectively;

FIG. 19 is a diagram showing the measurement result of characteristicsand showing the relation between the width t₁ of the tip of a magneticpole and a write density and between the width t₁ and overwrite in thehead of the present invention; and

FIG. 20 is a diagram showing the measurement result and showing therelation between an etching depth t₂ at the tip of the magnetic pole anda write density and between the etching depth t₂ and overwrite.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

This embodiment represents a fabrication method of a magnetic head inaccordance with the present invention and the result of studies onread/write characteristics. FIG. 1 is a perspective view of the poleportion of an induction type thin film head after machining by a focusedion beam etching process (hereinafter referred to as “FIB”) when it isobserved from an air bearing surface side. The material of a pole 102 isa permalloy having a saturation flux density of 1.0 T, and a gap layer104 and a protective layer 103 are made of alumina. The material of aslider 101 is zirconia. The track width of the magnetic head before FIBmachining is 10 μm and the pole thickness is 1.5 μm at an upper part and1.0 μm at a lower part. Since zirconia used as the slider material ofthe head this time is a non-conductive material, the sample undergoescharge-up during FIB machining and a trench cannot be formed accurately.Therefore, a ultra-thin layer of Au is formed on the slider surface byevaporation before FIB machining. Incidentally, this Au evaporationlayer can be removed by ordinary ion-milling or by polishing after FIBmachining. On the other hand, evaporation becomes unnecessary when asystem which irradiates an electron beam during FIB machining andneutralizes charge-up is utilized. FIG. 1 shows a sample having a trackwidth of 1 μm at both upper and lower parts and a machining depth of 2.0μm after FIB machining. The ion seed of the ion beam 100 used formachining is GaIn and an acceleration voltage and a beam current are setto 30 kV and 1.6 nA, respectively. The beam diameter at this time is 0.2μm.

Embodiment 2

A non-magnetic metallic material having a low specific resistivity suchas Cu is packed into the trench portion formed by FIB machining and aflux leaking from portions other than from the track portion defined bymachining can be reduced particularly in a high frequency range byutilizing an eddy current loss. This sample can be produced by a methodwhich carries out FIB machining in a W(CO)₆ atmosphere to form a W layerin the region to which FIB is irradiated, and conducts field plating byutilizing this conductive layer to form Cu. Besides this method, thesample can be produced by another method which uses Al having highconductivity, or the like, as the ion seed and forms a Cu layer by fieldplating utilizing the ion injection layer which is formed at the trenchportion of the sample by FIB machining. Here, the differences in thefield distribution and field intensity between the thin film head havingthe Cu layer, which is a magnetic shield layer and is formed at thetrench portion after FIB machining and a thin film head having thetrench portion under the as-formed state are measured by an electronbeam computerized tomography utilizing a Lorentz effect of an electronbeam. FIG. 2 shows the result when the distribution of a longitudinalmagnetic field Hx of the field distribution to be measured at 30 MHz inthe track width direction is measured at the center position of the gap.The track width of the head after machining is set to 1 μm in eachsample. It can be understood from this result that the leakage fluxleaking from the regions other than from the track can be reduceddrastically by forming Cu as the shield layer at the trench portion. Theeffect of this shield layer becomes greater with a higher frequency.Incidentally, the machining depth of the head used this time for themeasurement is 2 μm but the leakage field of the heads not having the Culayer formed thereon hardly changes even when the machining depth ismade greater than the value described above. On the other hand, FIG. 3shows the result when the frequency dependence of the maximum value ofHx is measured at the center position of the head magnetic pole, thatis, the gap, and at the center position of the track. It can beunderstood from this diagram that the effect of the Cu shield layerbecomes higher for the field intensity, too, with a higher frequency.

Embodiment 3

FIG. 4 shows the result of comparison of off-track performance between aself read/write thin film head whose track width is not coincidentbetween the upper pole and the lower pole and which is fabricated by theprocess of JP-A-59-178609, for example, and a thin film head obtained bysubjecting this head to FIB machining so that the track width of theupper pole is coincident with the track width of the lower pole with 0.1μm accuracy. The track width of the upper pole is 10 μm and the trackwidth of the lower pole is 13.5 μm before FIB machining, and the trackwidth is 10±0.05 μm for both poles after FIB machining. In thisexperiment, too, the Cu layer is formed at the trench portion of theslider rail machined by FIB. A spatter material having a coercive forceof 1,500 Oe and a film thickness of 0.06 μm is used for the measurementand the spacing is 0.1 μm. The recording density is set to 50 kFCI (FluxChange per Inch). It can be understood from the result shown in FIG. 4that the effect of alignment of the track edge portions of the upper andlower poles becomes remarkable when the off-track distance exceeds thehalf of the track width, and is effective for narrowing a track pitch.In this case, no change is observed in the read output and overwriteperformance before and after machining.

Embodiment 4

Next, the change of the read output per unit track width is measured byreducing the track width from 10 μm to 0.25 μm under the state where thedimensional difference of the track width between the upper and lowerpoles is kept below 0.1 μm. The result is shown in FIG. 5. The measuringcondition and the medium are the same as those used in FIG. 4. Here, theself read/write thin film head and the read/write head using an MR headfor reading are used. The machining depth of FIB is set to 2.0 μm forboth heads. It can be understood from the result shown in FIG. 5 thatwhen the track width is below 3 μm in the self read/write head, a dropin the read output is observed and this output drops to the half of theoriginal read output (the read output of the head having a 10 μm trackwidth) at the track width of 1 μm. It has been confirmed by theobservation with a Lorentz microscope of the recording track written bythe head of each track width that even when the track width of the headis 0.25 μm, the medium is recorded uniformly in the track width-wisedirection in response to the track width of the head. It is thereforebelieved that the cause of the drop of the read output when the trackwidth is reduced below 3 μm results primarily from the drop of the readsensitivity of the head. In the read/write head using the MR head forreading, on the other hand, the drop of the read output is not observedeven when the track width is reduced down to 1 μm and it is found thatat least 80% of the original output is obtained even when the trackwidth is reduced down to 0.25 μm. It has thus been confirmed that in thehead having the track width of 3 μm or below, the read/write head havingthe separate write and read heads is effective.

Embodiment 5

Next, FIG. 6 shows the result of the examination of the changes of theread output and off-track performance of the magnetic head which ismachined by changing the incident angle of FIB. The track width afterFIB machining is 3 μm and the machining depth is 2 μm. The medium usedfor the measurement of the read/write characteristics and the measuringcondition are the same as those used in FIG. 4. The abscissa in FIG. 6or in other words, the incident angle θ of the ion beam, represents thedeviation from a direction perpendicular to the air bearing surface ofthe head, and is set so that when the right-hand and left-hand portionsof the track are machined, the incident angles are symmetric withrespect to the track center, respectively. Here, an off-trackperformance index OFP is used as an index for evaluating off-trackperformance. This OFP is defined as follows:

OFP=x/(Tw/2)

Here, symbol X represents the off-track distance when the read outputdrops by 6 dB from the initial value when the head is tracked off and Twis the track width of the head after FIB machining. It can be understoodfrom this diagram that off-track performance gets deteriorated when theincident angle is 10° or more, whereas the read output drops at 0° orbelow and gets unstable at 20° or more. It can be understood from thisresult that the incident angle of the beam is set preferably from 0° toabout 10°. In this embodiment the shape of the head is set to anarbitrary shape by changing the incident angle of FIB, but machining ofthe head having an inclination at the track edge portion becomespossible by changing two-dimensionally the irradiation quantity ordevising a peculiar polarization method even when the incident angle is0°.

Embodiment 6

FIG. 7 shows the result of the examination as to to which extent theread/write characteristics change when the portions other than the poleportion of the head slider rail are cut off uniformly by FIB aftercompletion of a polish work. In the polishing process of the air bearingsurface of an ordinary thin film head, a machining step of about 20 toabout 30 nm is defined between the slider rail and the magnetic film ofthe pole. This machining step is eliminated by cutting off the sliderrail. Since the surface property of the slider rail changes hardly byFIB machining, it has been confirmed that floating characteristics ofthe slider does not at all change before and after this machining. Themedium and measuring condition used for the read/write characteristicsare the same as those described already. As a result of this FIBmachining, it has been confirmed that the read output can be improved byabout 16% at a recording density of 50 kFCI by cutting off uniformly theportions other than the pole portion of the slider rail by about 30 nm.

Embodiment 7

An ordinary thin film head for in-plane recording can be modified to asingle pole vertical head by utilizing FIB machining; hence, thisembodiment represents an example of such a modification. This machiningcuts off only the upper pole of an ordinary thin film head for in-planerecording to a certain extent. FIG. 8 shows the result of theexamination of the vertical recording characteristics of thepseudo-single pole vertical head obtained by this machining. The coilused hereby is buried in an alumina layer. The medium used formeasurement is a two-layered film medium of CoCr and permalloy and thespacing is set to 0.05 μm. Incidentally, a separate vertical head isused for reading from the relation of the pole thickness. It has beenconfirmed from this result that the recording density characteristicscan be improved because the recording mode changes from the in-planemode to the vertical mode when the machining depth of the upper pole isincreased. Here, a single pole head that can be used for both readingand writing can he fabricated by use of a photoresist pattern for anordinary thin film head for in-plane recording by optimizing thethickness of the upper and lower poles, respectively. In this manner thehead for in-plane recording can be converted to a head for verticalrecording by utilizing FIB machining.

Embodiment 8

Another embodiment of the present invention will be explained withreference to FIGS. 9A and 9B. FIG. 9A is a perspective view of aread/write head when viewed from the floating surface side and FIG. 9Bis a sectional view taken along line A-A′ in FIG. 9A. As can be seenfrom these drawings, the head in accordance with this embodiment isprovided with a write head 11 at the back of a read MR head 10. The pole12 on one of the sides of this write head serves also as one of theshield layers 2 of the MR head. The structure of the MR head is asfollows. A magnetoresistive sensor 3 and an electrode 4 for causing acurrent to flow are disposed between two soft magnetic members 1, 2 thatserve as the magnetic shield layer. First of all, a permalloy patternwhich is 2 μm thick and is a first shield layer 1 is formed on analumina titanium carbide substrate 5 on which an insulation layer madeof alumina is laminated. The shape of this first shield layer 1 isrectangular. Next, an MR sensor 3 is formed through the insulationlayer. This insulation layer uses alumina. This embodiment uses a shuntbias method as a method of application of a bias magnetic field which isnecessary for operating the MR sensor. Therefore, a 0.1 μm-thicktitanium film is laminated continuously as a shunt film on a 40 nm-thickpermalloy film and then the rectangular MR sensor pattern is formed byphoto-etching. Thereafter, a 0.2 μm-thick copper electrode 4 is formedon both sides except for the portion which will serve as a magneticsensitive region. Next, a second shield pattern 2 is formed through aninsulation layer. This shield pattern serves also as a first write pole12. A Co system amorphous soft magnetic film having a greater saturationflux density than permalloy is used in order to obtain a greater writefield. The film thickness is 2.5 μm. Alumina having a film thickness of1 μm is used for a gap layer 13. A coil 14 has five turns of copperhaving a film thickness of 3 μm. An etching 17 is then applied onto aslope portion on the floating surface side of a planarization layerthrough an insulation layer 16. Subsequently, a second write pole 15 isformed by use of a Co system amorphous soft magnetic film having a filmthickness of 2 μm in the same way as the first pole and then aprotective film is laminated. The substrate is thereafter cut andpolishing of the floating surface is conducted.

Part of the floating surface other than the portion which will become amagnetosensitive region is removed during the polishing step byphoto-etching technique which is employed ordinarily. First of all, anabout 3 μm-thick photoresist is coated on the floating surface and adesired resist pattern is obtained by effecting exposure. Recesses 7 and8 are formed by use of this resist pattern as a mask by ion millingwhich uses an Ar gas, in such a manner as to project themagnetosensitive region 9. Both of the MR head and write head portionsare shaped so that the width of the projecting portion 9 is 3 μm andthey are positioned on the same track.

In order to obtain a head having high read efficiency in the processdescribed above, it is preferred to project only the MR sensor portionwhich is not short-circuited by the electrode. To accomplish thisobject, the electrode pattern and the pattern for forming the projectingportion must be registered with a high level of accuracy at the time ofexposure and a narrow pattern is preferably disposed in the electrodelayer so that a registration marker is exposed on the floating surface.Furthermore, the width of the portion at which the electrode is notdisposed, or in other words, the gap between the electrodes, ispreferably greater than the width of projection in order to secure aregistration margin. In this embodiment the gap between the electrodesis 4 μm and the width of the projecting portion is 3 μm.

The embodiment described above uses the photoresist as the mask for ionmilling but can also use a metal mask or a carbon mask by use of amulti-layered resist method and a selective etching method.

FIG. 10 shows the sensitivity distribution (solid line in the drawing)of the head described in this embodiment in the track width direction incomparison with the sensitivity distribution (dash line) of the head nothaving the projecting portion defining the track width between theelectrodes at both ends in accordance with the prior art structure. Thedrop of the sensitivity of the head at the track edge is sharper in thehead of the embodiment of the invention and this represents thatinfluences from adjacent tracks are smaller.

As described above, the projecting portions of both the write and readheads can be formed simultaneously and accurately by carrying outetching from the floating surface, so that a position error does notoccur between the read and write heads and a read operation can be madeefficiently.

Though the embodiment described above uses the Co system amorphousmaterial as the pole material, other high saturation flux densitymaterials such as Fe system crystalline materials can be used, too.Though the width of the write head in the track width direction beforethe recesses are formed is equal to the width of the shield layer of theMR head, the former may be different from the latter so long as it isgreater than the width of the projecting portion.

Embodiment 9

Still another embodiment of the invention will be explained withreference to FIGS. 11A and 11B. This embodiment is substantially thesame as the first embodiment and has a write head at the back of the MRhead. However, the width of the projecting portion of the write head is4 μm, the width of the projecting portion of the MR head is 3 μm and thewidth of the read head is made smaller. If there is any positioningerror of the heads, the influences of noise from the adjacent tracksbecomes smaller when the read operation is made from a track having asmaller track width than the width of the written track, as is wellknown in the art. The track width can be changed easily by changing theprojecting width of the read/write heads by carrying out etching fromthe floating surface as is made in this embodiment. Accordingly, amagnetic head having suitable read/write track width can be fabricatedeasily.

All the foregoing embodiments use the shunt bias method as the method ofapplication of the bias field to the MR head but the present inventionis not particularly limited thereto and can employ heretofore knownpermanent magnet bias, soft-film bias, exchange coupled film bias usinga ferro-dimagnetic film, and so forth.

Embodiment 10

Still another embodiment of the present invention will be explained withreference to FIGS. 12A and 12B. In this embodiment the MR sensor 3 isdisposed between the poles 16 and 17 of the write head. The pole servesalso as the shield film of the MR head. In the drawings, the pole uses aCo system amorphous magnetic film having a high saturation flux densityand the film thickness is 2 μm. The bias field is applied to the MRsensor by causing a D.C. current to flow through the write coil. Forthis reason, the MR sensor is not provided with the shunt film butcomprises only the permalloy and the electrodes. The bias field can beapplied more easily if the MR sensor is disposed at a position deviatedfrom the center between the poles and in this embodiment, the ratio ofdistance between the poles and the sensor is set to 1:2. The rest of thestructure of the head and the machining method of the projecting portionof the floating surface are the same as those described in the foregoingembodiments.

According to this embodiment, the MR sensor is disposed between thewrite poles and the write poles serve also as the shield layer.Therefore, the width of the write pole shield layer coincides with thewidth of the projecting portion of the MR sensor and there can thus beobtained a magnetic head free from the positioning error between theread and write tracks.

The embodiments Nos. 8, 9 and 10 represent the structure in which partof the write pole serves also as the shield layer of the MR head but thepresent invention can also be used for a write/read head in which thewrite poles and the shield layers are separated completely.

Embodiment 11

FIG. 15 shows an example of the section of the magnetic core portion ina conventional thin film magnetic head. As shown in the drawing the thinfilm head comprises a magnetic core consisting of an upper magnetic film10 a and a lower magnetic film 10 b and a conductive layer coil 20sandwiched between these films. The write/read operation is made whenthe pole portion P at the tip of the core travels while opposing amedium.

Each of the magnetic pole film and coil is formed by depositing amagnetic layer and a conductive layer on a substrate by spattering, orthe like, and then carrying out patterning by ion milling, or the like.

The magnetic core comprises the pole tip P that opposes perpendicularlythe magnetic recording medium, the slope portion S from which the gapbetween the upper and lower magnetic films starts expanding graduallyand the back region B which is disposed through the conductor layer. Inorder to improve read/write efficiency of the head and to preventmagnetic saturation, the back core B has preferably a sectional areawhich is as great as possible and in order to effect high densityread/write operations, the sectional area of the tip of the pole ispreferably as small as possible. As to the planar shape, a design hasbeen made so that the magnetic film of the back core B expands graduallywith respect to the rectangular pole tip portion P having a widthsubstantially equal to the track width opposing the medium, as disclosedin JP-A-55-84019.

In conjunction with the sectional structure, a method of preventingmagnetic saturation has been proposed by laminating further a magneticfilm 10 c on the upper magnetic film 10 a as indicated by dash line inFIG. 15 so as to enlarge the sectional area of the back core region.Since the slope portion S has an inclination, however, it is difficultto superpose completely the magnetic film 10 c on S and P while leavingonly the pole tip α on the medium opposing surface. Therefore, thethickness of the upper and lower magnetic films 10 a and 10 b must beincreased in order to prevent magnetic saturation at the tip regions Pand S which are believed to affect greatly read/write efficiency.

In accordance with the prior art technology described above, the filmthickness d₁ of each of the magnetic films 10 a and 10 b is uniform inthe back region B, on the slope portion S and in the tip region P. Forthis reason, the prior art technology involves the problem in that ifthe thickness of the pole magnetic film is increased for accomplishingthe object described above, the width t₁ at the pole tip becomes great,as well. In other words, even when the magnetic bias g₁ is reduced, t₁cannot be reduced, so that a sharp field cannot be generated from thetip of the pole and there is an inevitable limit to the improvement inrecording density.

The object of this embodiment is to improve the magnetic core shape ofthe head in order to make the read/write operation in a high density,with high resolution and moreover, efficiently.

This object can be accomplished by cutting off the side surface of theupper and lower pole magnetic films opposite to the magnetic gap andreducing the film thickness at the pole tip without changing themagnetic gap width.

In FIG. 14, the film thickness d₁ of the back region B of the polemagnetic film is 1 μm, for example, and the film thickness t₁ of the tipregion P on the medium opposing surface side is 0.5 μm, for example. Thefilm thickness is sufficiently great in the back region B, the slopeportion S and the region of the tip P on the S side, and magneticsaturation does not occur. At the same time, a sharp field is generatedfrom the medium opposing surface of the tip to conduct high densityrecording. Accordingly, read resolution can be improved and highefficiency and high density magnetic recording become thus possible.

FIG. 13 is a plan view of a thin magnetic film head showing stillanother embodiment of the present invention. Reference numeral 10represents a magnetic core obtained by patterning a permalloy oramorphous magnetic film, which is formed on a substrate by spattering orthe like, by ion milling using a photoresist as a mask. Referencenumeral 20 represents a conductor coil. Upper and lower magnetic layersof the magnetic core come into mutual contact at 11 and define a yokestructure and the conductor coil 20 interposed between these upper andlower magnetic layers is completely insulated by a resin insulationlayer.

FIG. 14 is a sectional view taken along line A-A′ of the magnetic coreshown in FIG. 13. This embodiment uses the amorphous alloy for themagnetic film. The upper magnetic film 10 a comprises the pole tip Pwhich opposes perpendicularly the magnetic recording medium, the slopeportion S from which the gap between the upper and lower magnetic filmsstarts expanding gradually and the back region B disposed through theconductor layer. The film thickness d₁ of the upper and lower magneticfilms in the head back region B is 1.0 μm and the length of the pole tipP corresponding to the gap length is g₁=0.5 μm. The gap depth is g₂=0.8μm. A focused ion beam (FIB) is irradiated from the directionrepresented by arrow D in parallel with the arrow so as to etch the poletip to a film thickness of t₁=0.5 μm. The etching depth from the mediumopposing surface is t₂=0.5 μm so that the pole film thickness changes ata position close to the medium from the slope portion S. Etching withabout ±0.1 μm accuracy becomes possible in both directions of width anddepth by use of FIB. Such a core does not cause magnetic saturation atportions other than part of the tip P at which the film thickness issmall and at the same time, a sharp field can be generated from the tip.Accordingly the read/write operation can be made highly efficiently withhigh resolution.

FIG. 18 shows the result of the measurement of frequency characteristicswhen the read/write operations are carried out practically by use of thehead having the pole magnetic film of this embodiment and theconventional head having a uniform thickness for the pole magnetic film.

In the conventional head, comparison is made by changing the thicknessd₁ of the pole magnetic film to 1 μm and 0.5 μm. A γ-Fe₂O₃ coated mediumhaving a film thickness of 0.4 μm is used as the recording medium andthe spacing is 0.3 μm. As shown in the diagram the frequencycharacteristics are poor in the film whose film thickness d₁ is 1 μm anduniform, and the output drops at about 10 kFCI. In the case of the filmwhose film thickness d₁ is 0.5 μm and uniform, the read output drops byabout ⅓ in comparison with the head having d₁ of 1 μm. In contrast, whenthe head of this embodiment is used, higher output and higher frequencycharacteristics can be obtained. For example, the read output isincreased by about twice to about thrice at 20-60 kFCI in comparisonwith the conventional head.

FIG. 7 shows the result of the measurement of the recording density andoverwrite performance in the head of this embodiment when the filmthickness t₁ at the tip of the pole is changed. The read/write conditionis the same as described above. The recording density drops when t₁ isincreased but overwrite performance can be improved. Both recordingdensity and overwrite performance are satisfactory when t₁ is from 0.3to 0.8 μm.

FIG. 20 shows the result of the similar measurement when the etchingdepth t₂ at the tip of the pole is changed. When t₂ is increased, therecording density is improved but overwrite performance drops. Bothrecording density and overwrite performance are satisfactory when t₂ isfrom 0.3 to 0.8 μm.

Embodiment 12

FIGS. 16 and 17 show still another embodiment of the present invention.In the pole magnetic film shown in FIG. 16, only the film thickness atthe tip of the upper magnetic film 10 a is reduced in the same way as inthe head shown in FIG. 14. In the pole magnetic film shown in FIG. 17,on the other hand, FIB is irradiated obliquely from the direction ofarrow B, B′ so that the film thickness at the tip becomes graduallygreater. Since both employ the structure wherein a sharp field isgenerated from the tip to effect high density recording and the filmthickness is sufficiently great in the back region to prevent magneticsaturation, high density magnetic recording can be made highlyefficiently.

As described above, the present invention can provide a magnetic headhaving a simple structure which improve noise characteristics resultingfrom adjacent tracks. Furthermore, the present invention makes itpossible to position the write head and the read head with a high levelof accuracy.

Since even a head having a track width of 1 μm or below can befabricated at a high yield, the present invention is particularlyeffective for a head for a magnetic disc apparatus which has a largememory capacity and for which high speed transfer of data is necessary.

Since the present invention can provide a thin film magnetic head havinga large read output and a high write density, the invention can improveperformance of a magnetic memory device.

What is claimed is:
 1. A magnetic head comprising: a reproducing headincluding a magnetoresistive sensor and a write head including an uppermagnetic pole formed over a gap layer and a lower magnetic pole formedunder the gap layer, wherein trench portions or recessed portions areformed in surfaces facing a magnetic disk medium of said reproducinghead and write head, said trench or recessed portions are filled with amagnetic shield material, widths of said upper magnetic pole and lowermagnetic pole are defined by said trench or recessed portions filledwith the magnetic shield material, and a track width of said reproducinghead is defined by said trench portions or recessed portions filled withthe magnetic shield material.
 2. The magnetic head according to claim 1,wherein said magnetic shield material is a non-magnetic material.
 3. Themagnetic head according to claim 1, wherein said magnetic shieldmaterial is an electrically conductive material.
 4. The magnetic headaccording to claim 1, wherein a difference between the widths of saidupper magnetic pole and said lower magnetic pole are no greater than 0.1μm.
 5. The magnetic head according to claim 1, wherein said trenchportions or recessed portions are focused ion beam etched trenchportions or recessed portions.